SAN BRUNO — The executive who headed PG&E’s utility unit at the time of the deadly San Bruno explosion will retire at year’s end, PG&E said Tuesday.

Separately, PG&E has released new emails shedding light about its ties to the state Public Utilities Commission, a cozy connection that is being investigated by a federal grand jury.

Christopher Johns, president of Pacific Gas & Electric, the utility arm of PG&E, was appointed president of Pacific Gas & Electric in August 2009, 13 months prior to a fatal explosion of natural gas in September 2010 that killed eight and demolished a quiet San Bruno neighborhood.

His record was praised by executives, who said they would work on a succession plan before Johns leaves at the end of December.

“Record electric reliability, international recognition for gas safety performance and the highest customer service ratings since 2009” were among the accomplishments over which Johns presided in 2014, said PG&E Chairman and CEO Anthony Earley.

Johns also was president of Pacific Gas & Electric at a time when the company opened a state-of-the-art control complex in San Ramon that serves as the utility’s nerve center for its gas operations, a major step toward making gas distribution safer and more reliable and meeting recommendations issued by the National Transportation Safety Board following the San Bruno explosion. During Johns’ tenure following the explosion, PG&E pleaded not guilty to a 28-count federal criminal indictment that claimed the utility violated pipeline safety rules and obstructed justice, was ordered by the PUC to pay a record $1.6 penalty for causing the San Bruno disaster, and suffered multiple security breaches at its Metcalf substation in south San Jose.

The new emails that PG&E released this month reinforce a picture of a state PUC that has accommodated the wishes of PG&E.

“Up and down the management chain at the PUC, people are being leaned on by PG&E, they are being intimidated,” said Loretta Lynch, a former PUC commissioner who is a harsh critic of the state agency’s ties to major utilities in California. “The culture at the PUC is to go along to get along, with the active complicity of a number of commissioners” at the state agency.

In one email, written in March 2014, former PG&E regulatory executive Brian Cherry wrote about a case involving the Diablo Canyon Nuclear Plant that was being handled by PUC Administrative Law Judge Stephen Roscow. Michael Florio was the PUC commissioner assigned to oversee the case.

“I spoke with Florio about Roscow,” Cherry wrote. “Mike (Florio) believes there is no need to bump Steve if he is the assigned commissioner. He understands Steve’s bias.”

“I would never use a word such as ‘bias’ regarding a respected colleague such as Steve Roscow,” Florio said in a response to this newspaper. “Mr. Cherry’s imagination apparently got the better of him — again.”

Separately, a federal grand jury has launched a fresh probe into the cooperation between the PUC and PG&E.

“There is an ongoing grand jury investigation into PG&E’s relationship with the PUC,” U.S. attorneys Kim Berger and Hallie Hoffman wrote in a May 15 letter to the attorneys who are representing PG&E on its criminal case, according to documents on file with the U.S. District Court in San Francisco.

The current criminal case is set to go to trial in 2016.

“The disclosure about the grand jury looking into back channel communications between PG&E and the PUC suggests the federal prosecutors are going after individuals this time,” said state Sen. Jerry Hill, whose San Mateo County district includes San Bruno.